The subject invention is directed to the art of electrical fuses and, more particularly, to an electrical fuse that is particularly adapted for use in motor vehicle applications.
Electrical fuses of the general type under consideration are commonly used in the automotive technical field. In particular, cut-out type fuses are currently employed in many applications. Cut-out fuses are adapted to interrupt a current supplied to one or more succeeding or downstream electrical consumers by melting a fusible zone when the current exceeds the nominal rated current of the fuse.
One disadvantage of cut-out fuses, however, is that they require a high intensity of current, typically significantly above the nominal current, to flow for a relatively long period of time before the fuse melts. As a consequence, cable carrying power between the fuse and electrical consumers succeeding or downstream of the fuse must be appropriately over-dimensioned or oversized in order to avoid over-current conditions and cable fires which have the potential of endangering the motor vehicle.
In addition to the above, other problems associated with electrical fuses of the type presently available include arcing phenomenon generated by the fuses when they melt and open the circuit. The arcing can have an interfering electromagnetic effect on the motor vehicle.
Yet another problem associated with meltable fuses is that they require a method or structure for screening off the fuse in order to prevent molten metal droplets produced from the melted portion of the fuse from migrating into other electrical components or circuits where they can cause shorting or other electrical damage.
In contrast thereto, it is a primary object of the present invention to provide an electrical fuse that is particularly adapted for use in motor vehicle applications that requires practically no over-dimensioning of the succeeding or downstream electrical cables and which does not generate any electrical arcing or sparks when the current is interrupted.
The subject invention provides an electrical fuse apparatus that overcomes the above-noted problems and results in a device that interrupts electrical current without producing undesirable electric arcing or molten metal droplets that are found to be damaging in motor vehicles. Further, for all practical purposes, the subject fuse apparatus enables the use of electrical cables that are precisely sized to carry only the electrical currents that are anticipated to be required by the electrical consumers rather than oversized for carrying excess current that has been the practice in the past.
In particular, and in accordance with one aspect of the invention, there is provided a fuse apparatus for selectively interrupting a load current flowing between a pair of associated conductor leads. The fuse apparatus includes at least two spaced apart electrically conductive contact elements, a fuse element, and an electrically conductive connection material. The at least two spaced apart electrically conductive contact elements are each operatively connected with the associated electrical conductor leads. The electrically conductive connection material selectively holds the fuse element across the at least two contact elements to allow a load current to flow between the pair of associated conductor leads. In accordance with the preferred embodiment of the present invention, the connection material is adapted to electrically disconnect the fuse element from the spaced apart electrically conductive contact elements when a temperature of the connection material exceeds a predetermined threshold temperature.
In accordance with a more limited aspect of the invention, the electrically conductive connection material has an intrinsic electrical transition resistance characteristic whereby the connection material develops a temperature in proportion to an intensity of current flowing therethrough.
By connecting the fuse element to the pair of spaced apart electrically conductive contact elements using a meltable electrically conductive connection material, the connection material melts and thus separates the fuse element from the contact elements before the fuse element proper has an opportunity to possibly melt and scatter molten metal or generate electrical arcing interference. Preferably, the fuse element is a cut-out fuse of the type commonly available in the art and described above.
In accordance with a still further aspect of the invention, the electrically conductive connection material disposed between the fuse element and the pair of contact elements becomes soft at elevated temperatures and melts when its temperature exceeds a predetermined temperature. In that manner, the fuse element is separated from the contact elements without arcing or molten droplets being formed. Preferably, the predetermined temperature is reached when the current flowing through the connection material surpasses the rated current of the fuse. Overall, this results in the benefit of a substantially lower amount of heat needed for triggering the fuse. That is, the subject fuse reacts to small increases in power surpassing the rated current of the fuse. In that regard, the subject invention is more sensitive to currents that are only slightly above the rated current of the system. Thus, the drawbacks of the melting process at high temperatures typically found in fuses in the past are avoided.
In accordance with yet a still further aspect of the invention, the connection between the fuse element and the contact elements is established by means of soldering. In this manner, interruption of the load current by separation of the fuse element from the contact elements is readily obtained when the solder melts. Preferably, in accordance with the present invention, this takes place at temperatures of approximately 180xc2x0. Accordingly, any danger of producing arcing which is promoted in prior art cut-out fuses by the occurrence of high temperatures, is practically non-existent in the present invention.
According to one embodiment of the invention, the fuse element is acted upon by the force of a resilient spring element, independent of the position of the fuse, so that during the melting or softening of the connection between the fuse element and the contact elements, the fuse element is lifted or separated from the contact elements, thus interrupting the flow of load current through the fuse system.
In accordance with yet another aspect of the invention, in one embodiment, the fuse apparatus is provided with an additional heating portion. The heating portion is included to obtain an interruption in the flow of current to the electrical power consumer in the presence of a given or varying nominal current. More particularly, the heating is performed so that the immediate environment of the connections is heated between the safety element and the contact elements. In the preferred mode, heating takes place by generation of an additional current through the fuse element and through the one or several contact elements. The additional current utilized for heating, is superimposed on the load current supplied to the succeeding or downstream electrical power consumers.
For generating the additional heating current, the power consuming device can be dimensioned in such a manner that with any direct connection with a battery using the fuse, a theoretically inadmissible high current would result. More particularly, the excess current that is used for heating is discharged via a resistor which is preferably connected with one of the connection contacts or to the fuse element itself. The discharge current and heat generated thereby is preferably dissipated using a mass such as a heat sink, for example. The resistance value of the bleeder resistor through which the additional heating current flows, is used to control the temperature of the connections between the fuse element and the contact elements during normal fuse operation. Accordingly, the rated current of the fuse is established by means of the resistance value of the bleeder resistor.
In addition to the above, heating can also be performed in such a manner that the temperature of the connections or of the contact elements, or still further of the fuse element proper, is sampled or otherwise read and maintained in a closed loop control. As an alternative to the above embodiments, in accordance with yet another alternative embodiment, the ambient temperature is sampled and the heating of the fuse element and connection material is executed in accordance with the sensed ambient temperature. According to this method, the rated fuse current is obtained based on ambient temperature.
Still yet further in accordance with the present invention, the fuse is designed in such a manner that the resistance value between the connection contacts of the fuse, which is essentially determined by the intrinsic resistance values of the fuse element and/or the contact elements, is used as a shunt to generate a voltage signal and therefrom calculate the flow of current to one or more succeeding or downstream electrical current consumers. To that end, the contact elements and the connections are formed to have a desired resistance value.
In accordance with yet another aspect of the invention, in a total system for protection of electrical current consumers, the voltage drop across the subject fuse is sensed, the current flowing therethrough to the current consumers is then determined and, when the threshold current is surpassed, an active interruption element is targeted to cut off the flow of current to the consumer. In such an arrangement, the fuse is formed in such a manner that a controllable switch, such as, for example, a relay or the like, is connected with the contact element or fuse element. The controllable switch is positioned in that manner so that, if excessive threshold current is detected, targeting or control of the controllable switch is initiated in such a fashion that a major portion of the current, or its entirety, is discharged, preferably against a mass such as a heat sink or through a suitably sized bleeder resistor.
With the above form of design, there is assured on one hand, that the detected, inadmissibly high load current to the electrical power consumers is partially or completely reduced to zero. Also, there is an assurance that a high current is produced through the fuse which, in turn, leads to triggering the fuse. In this fashion, a fuse having an extremely quick reaction time is created which, furthermore, ensures an irreversible separation of the electrical current consumer from the power source.
In addition to the above, instead of the targetable electrical trigger heating, another embodiment of the invention employs a self-triggering or targetable heating element of a different type. One preferred example is a heating element based on an exothermic chemical reaction. Such an electric heating element is activated either by means of an electrical signal or by triggering an exothermic reaction that starts from a predetermined temperature. As an example, the heating element is preferably provided in the immediate vicinity of the connections between the contact elements and the fuse element so that, upon excessive rated current flowing through the fuse leading to an increased temperature, the threshold temperature of the trigger heating element is surpassed and heating is triggered or initiated. In that embodiment, even with relatively low excess of rated current, it is possible to achieve very rapid triggering of the fuse.
As can be seen from the foregoing, a primary object of the invention is to provide a fuse apparatus that separates electrical power consumers from a source of electrical power without generating electrostatic discharge caused by arcing and without producing molten metal contaminants.
A further object of the invention is to provide a fuse apparatus that enables the use of conductors having the minimum size required to meet the load demands of the electrical power consumers.
A still further object of the invention is the provision of a fuse apparatus that has a quick reaction time to interrupt the flow of excessive load current before any damage can be done to the electrical current consumers of the conductors carrying the load current.
Still other advantages and benefits of the invention will become apparent to those skilled in the art upon a reading and understanding of the following detailed description.